1. Field of the Invention
This invention relates to an applanation tonometer for providing a measurement of the intraocular fluid pressure (IOP) inside the eye of a human or animal patient. The applanation tonometer herein disclosed has means responsive to both the contact force of the tonometer against the cornea and the touch contact area of the tonometer with the cornea so that paired force and area data is collected, whereby IOP can be accurately measured with minimal dwell time on the cornea and discomfort to the patient.
2. Background Art
A tonometer is a non-invasive instrument which has heretofore been used to measure pressure or tension in human or veterinary tissues. In the human body, intraocular fluid pressure in the eye (IOP) is measured to provide basic information for the diagnosis and treatment of glaucoma and related eye disease.
Ease of application, accuracy and sterility of a tonometer are paramount in medical applications. One instrument which is known to provide highly accurate IOP measurements is the Goldmann applanation tonometer (GAT). A quasi-scientific basis to acquire accurate IOP measurements is referred to as the Imbert-Fick principle. According to this principle, IOP is determined by a calculation of the contact force applied by a tip or the GAT against the cornea divided by area of contact. That is, determining IOP with the GAT relies upon the contact tip covering an applanation area to a fixed diameter of 3.06 mm. The applied force necessary to reach the requisite applanation area is adjusted manually by the healthcare physician or technician. Because the dwell time of the contact tip on the cornea is typically measured in seconds, at topical anesthesia is necessary for the eye. Force and area measurements made by the GAT after multiple touch contacts with corneas of eyes with a range of IOPs form the basis of a nomogramn-derived inference of IOP with respect to a compilation of direct cannula measurements of a population of animal and human eyes.
On occasion, the moving parts of the GAT may jam which can interfere with the effectiveness of the IOP testing. Moreover, the relatively long dwell time required for the contact tip to press correctly against the cornea and the need to apply a topical anesthesia as a result thereof may increase patient discomfort and tissue safety concerns. In this same regard, it would be preferable to limit data acquisition to a single light touch in most cases while providing an instantaneous confirmation to the healthcare professional of either a successful or an unsuccessful pressure test of a patient's eye.